1. Field Of The Invention
This invention related to production of hydrocarbon fluid from a subterranean formation, and more particularly to a method for reducing water production from a gravel packed well penetrating the formation.
In typical water drive reservoirs in the Gulf Coast area, water encroachment from below the hydrocarbon zone leads to operating problems, and eventually makes the wells uneconomical to operate. There has been a continuing need for an economical and efficient method for reducing water production from such wells.
In a typical gravel packed well, a perforated section of production tubing is wrapped with a screen, and the wrapped section is located adjacent a hydrocarbonproducing zone. Channels between the screen and tubing permit flow from the screened interval to the tubing perforations. The annulus between the wellbore wall and the screen around the tubing is then "packed" with sand of a particular size range. The sand is commonly referred to as gravel, although it is typically a 40/60 mesh sand. The sand or "gravel" is intended to prevent formation damage during production, and is sized so that it will not pass through openings in the screen around the production tubing. As the well is produced, the water level encroaches upwardly to the gravel packed zone, and remedial procedures which isolate the encroaching water from the production tubing are necessary.
2. The Prior Art
Cement has been used in the past to isolate the water zone from the production tubing, but there are problems with use of cement for this purpose.
First, when the cement is dump bailed into the wellbore, a malfunction of the bailer can inadvertently bridge off cement in the blank (unperforated) tubing above the gravel pack interval. The cement must then be drilled out to clear the tubing. Second, if the cement formulation is not correct, the cement may not completely penetrate the perforated tubing and may fail to block off channels between the tubing and the gravel pack screen. Third, even if the cement effectively blocks the channels between the tubing and the screen, water still flows upward through the gravel packed annulus.
Recently, a procedure for isolating the water zone in a gravel packed well by placing a settable epoxy resin in the lower part of a gravel pack interval has been developed. This procedure is described in U.S. Pat. No. 4,972,906 issuing Nov. 11, 1990 by S. J. McDaniel. This procedure has met with some success, but presents problems when the interval to be isolated is long, or when there is open casing below the gravel pack. In either case, an excessive amount of resin is required, particularly when dump bailers are used to place the resin.
A method of recompleting wells is described in U.S. Pat. No. 3,208,525 to J. A. Caldwell et al. In that method, a stop device or bridge plug is placed in a cased well above a lower producing zone, and gravel and sand are placed on top of the stop device. An epoxy resin is then placed on top of the sand and gravel to isolate the lower producing zone form an upper producing zone. The procedure differs from that of the present invention in that it seals off an entire producing zone by forming a plug in the well casing, and it is not intended to seal off the lower portion of a gravel packed well.